MOJAVE, Calif. — The SpaceShipOne rocket plane landed safely here Wednesday after a successful tilt-a-whirl start to its bid to win a $10 million prize for private spaceflight.

The craft fulfilled the first part of the requirement for winning the Ansari X Prize by going beyond the 100-kilometer (62.5-mile) mark, the internationally recognized boundary of outer space.

Radar readings from nearby Edwards Air Force Base indicated that SpaceShipOne topped out at 337,500 feet in altitude (63.9 miles or 102.9 kilometers), said Gregg Maryniak, executive director of the St. Louis-based X Prize Foundation and a member of the judging committee.

Under the X Prize rules, SpaceShipOne must fly above 100 kilometers once more within two weeks. The second flight was tentatively scheduled for Monday.

"One down, one to go," Peter Diamandis, the X Prize Foundation's founder and president, said at a postflight news conference.

Wednesday's flight started routinely, with SpaceShipOne rising from the runway at Mojave Airport hooked to the underbelly of its White Knight carrier airplane. But after SpaceShipOne separated from the White Knight and lit up its rocket engine for the upward boost, the plane went into a dramatic roll.

Video imagery showed the plane corkscrewing at more than 10 revolutions per minute before veteran test pilot Mike Melvill brought it back under control. The engine had been expected to fire for 90 seconds, but ground controllers told Melvill to shut down the motor early. Melvill took a couple of extra seconds, ensuring that SpaceShipOne would hit 100 kilometers.

“We actually were asking him to go ahead and abort, to shut it off to where he wouldn’t have gone (to the required altitude),” the spaceship's designer, Burt Rutan of Mojave-based Scaled Composites, said after the flight. “He stayed in there just for a handful of seconds more.”

Melvill said that he shut down the motor 11 seconds early, and that otherwise the craft could have risen another 4 miles (6 kilometers) or so.

'Victory roll'
It was the second challenging spaceflight for Melvill, who earned his astronaut wings during SpaceShipOne's
history-making mission
in June. After Wednesday's flight, Melvill made light of the roll.

"A victory roll at the top of the climb is important for an airshow pilot," he told reporters from the runway. "Did I plan the roll? I'd like to say I did, but I didn't."

X Prize rival Eric Meier of Space Transport Corp. watched the live video of the roll along with hundreds of other VIPs at Mojave Airport.

"Didn't look like a tourist flight," he deadpanned. "That's not to say that they can't smooth it out."

Indeed, once the craft bent its wings into a stabilizing position, the ride became smooth, and Rutan said the re-entry was "very perfect, smooth, straight." As the airport crowd cheered, SpaceShipOne glided back down to a trouble-free landing, then was towed around the runway for a victory lap with Melvill standing on top.

Rutan said his Scaled Composites team was looking into the potential causes of the roll.

Melvill said the spacecraft performed flawlessly, and speculated that he may have stepped on a rudder panel when he shouldn't have. "I'm not sure what kicked it off ... it's probably something I did," he said. However, Rutan noted that significant wind shear might have contributed to the roll.

During the June flight, Melvill had to cope with wind shear as well as a control-system glitch and a descent at almost 5 G's of acceleration — more than shuttle astronauts typically experience. After that outing, Melvill said he didn't plan to fly SpaceShipOne again. But Rutan said Melvill had to be pressed into service two weeks ago when the originally designated test pilot had a medical emergency.

Rutan said the precise timing of the second X Prize flight would depend on the analysis of the roll problem, although the most likely day still appeared to be Monday.

After Wednesday's flight, Melvill voiced reluctance about taking on the second X Prize flight and said he'd like to give one of his fellow test pilots at Scaled Composites a turn at the controls. "I feel like I'm grabbing all the flights ... but of course if no one else wants to fly it, I'll be happy to do it," he said at the postflight news conference.

The crowd of spectators for Wednesday's launch was smaller than it was for the June flight, which marked the first time a privately developed craft reached outer space. There was less history at stake this time around. However, if the next flight hits the 100-kilometer mark, it would earn $10 million for Mojave Aerospace Ventures, a partnership involving Rutan's Scaled Composites and Seattle billionaire backer Paul Allen.

Allen has spent more than $20 million on SpaceShipOne, and he said Wednesday that the X Prize proceeds would serve as partial compensaton for the venture's expenses. A newly announced licensing deal with the British-based Virgin Group, aimed at creating a new fleet of suborbital spaceships based on SpaceShipOne technology, would also help balance the books.

Mementos riding along
This was Melvill's second dose of spaceflight, and he marveled once again at the blackness of space and the views of Earth. "Now, that was fun," he said. "That’s why I work at Scaled, to do fun things. … That was a really good ride."

At the top of the ride, he said he was too busy stabilizing the spacecraft and taking pictures to think about stunts like releasing M&M candies in the weightlessness of space, as he did last time. Ironically, M&M was one of the new X Prize sponsors for Wednesday's flight.

Nevertheless, the flight had its own personal touches: During its two prizeworthy flights, the spacecraft is required to carry almost 400 extra pounds (180 kilograms), to represent the weight of two passengers. Rather than loading up the craft with lead weights, Scaled Composites' ground crew packed the seats behind the pilot with video equipment, a flight monitoring device known as the "Gold Box" and mementos from team members.

Rutan said employees had to sign forms promising that they wouldn't sell the items that were flown.

Among the items: photos, personal tools from toolboxes, tree seedlings, a teddy bear for a British charity, Rutan's 1961-vintage college slide rule, an heirloom watch and a copy of "The Spirit of St. Louis," Charles Lindbergh's book about his 1927 solo trans-Atlantic flight. That flight made Lindbergh the winner of the $25,000 Orteig Prize, which in turn provided the inspiration for the X Prize.

Rutan said an even more personal payload was added just before the flight: the ashes of his mother, Irene Rutan, who died four years ago.

"We rounded up her ashes, and she flew today," Burt Rutan said, with his eyes misting up.